The invention concerns an apparatus for introducing a first fluid into a second fluid which is flowing in a pipe, which apparatus consists of a pipe-shaped body with a through-flow channel for the said second fluid of essentially constant cross-sectional area, one or more chambers which extend round at least the majority of the circumference of the through-flow channel along at least a part of its longitudinal extent, a connection for supplying the first fluid to the said chambers from a pressure source, in which a series of through-holes is arranged in the said pipe-shaped body in the region of the said one or more chambers, through which holes the first fluid can be directed into the second fluid which is flowing through the said through-flow channel under the influence of the difference in pressure between the said chambers and the said through-flow channel.
The invention is advantageously applied to the admixing of steam into a flow of cellulose pulp.
Apparatuses of the type mentioned above are known, see for example SE 468 341 and SE 502 393. The apparatus described in SE 502 393 is used primarily as a mixer in the bleaching departments in the cellulose factories for the admixing of steam into a pulp suspension in order to raise its temperature to a level which is required to ensure that a specific reaction takes place with the desired speed in a subsequent bleaching step. The apparatus can give good admixing of steam into the suspension, but it is difficult to control the quantity of steam needed for temperature control without reducing the effectiveness of the admixing at the same time. The steam admixing is regulated conventionally by means of a valve in the steam pipe to the said chamber. However, as the steam supply is throttled to reduce the steam introduction, the pressure in the chamber also falls and hence also the pressure difference between the inside of the chamber and the pulp suspension in the pipe. This implies, in turn, a reduction in the speed of the steam, as it enters the pulp through-flow pipe, and thereby also the penetration of the steam into the pulp suspension.
A characterizing feature of SE 468 341 is that the through-flow pipe is made as a narrow, ring-shaped passage for the second fluid, which is considered to promote a good admixing effect. However, without taking a position on whether this idea is correct or not, or whether the possibility only applies under certain conditions, it can be observed in practice that the construction entails certain problems. This is probably due to the fact that the first fluid, when it is injected at high speed into the second fluid flowing through the narrow space, interacts with the constricting body installed in the through-flow channel and that, probably due to resonance phenomena, serious vibration can occur in the apparatus.
Moreover, another disadvantage with existing apparatuses is that an uneven temperature distribution in the pulp suspension after steam injection can arise. Sometimes temperature variations of about 10xc2x0 C. have been recorded between the upper and lower points in a cross section of the downstream pipe. Large temperature differences are obviously a major disadvantage when working with bleaching chemicals which are often very temperature sensitive, as for example hydrogen peroxide. Further, apparatuses of the existing type are relatively heavy. Since the material normal used is high-quality stainless steel, and, in addition, as the apparatus is relatively difficult to manufacture, the total cost for the apparatus is correspondingly high.
The purpose of the invention is to provide an apparatus that is not burdened with the limitations or disadvantages mentioned above. One object of the present invention is to provide an apparatus that gives good admixing of the first medium into the second medium and to ensure that good heat distribution is obtained in the downstream pipe, i.e. that very small temperature of differences are obtained in an arbitrarily chosen cross section of the downstream pipe.
Another positive effect of the apparatus is the generation of relatively little vibrations and provision of a good facility for adjustable and controllable admixing of a first medium into a second medium.
Further characteristics, aspects and advantages of the invention are presented in the following description of a preferred embodiment.